[TheForge] Re: lamp shade

[Chris Worsley]

Hmmm. . . .

Perhaps the need for fomulae is needed by some, but my solution to the 
situation is to just do it.
I forget, but wasn't this made from angle iron? That is what I recall 
without looking back. So - -
Clamp down the four base pieces on the layout table as close as possible 
to proper postion, and start scribing and grinding the angles needed on 
the disc grinder.
Tack.
Do the same for the top rectangle.  Jig up the distance between the 
bottom and top and measure upright corner pieces.
In the past it has always been a combination of eyeball & scribe & grind 
on the disc grinder as I go.  I have never made this shape, but have 
made guitar stands, lamps,  and other angled items in this manner.
I used the disc grinder so I can have a firm base on the table that is 
angle adjustable.

Clamp with blocks the corners before final welding. File and sand clean 
all welds. Chewing gum welds are not acceptable.


Chris
AZ

Mike Spencer wrote:

>Janet> Okay, that sounds good, but what's the formula for figuring it
>Janet> out?
>
>[scribble scribble...scritch scritch scritch scribble....]
>
>
>Okay, first lets get straight what goes into the formula. Here's
>what one panel of the truncated cone looks like:
>
>
>          ------------------------        ------
>  Side   /                        \          ^
>   S--->/                          \         |   Height H measured at right
>       /                            \        |   angles to the upper and 
>      /                              \       |   lower edges.
>     /                                \      v
>     ----------------------------------    ------ 
>
>
>(In case your mail reader messes up the ASCII sketch: S is the length
>of one of the angled sides.  H is the right-angle distance between the
>two parallel sides.)
>
>
>The angle we're looking for we'll call 'A'.  Then,
>
>                    sqrt(2) S
>  1/2  A = arcsin  ----------
>                      2   H
>
>That is, multiply the square root of 2 times S, divide that by 2 times
>H.  Then take the inverse sine of that number.
>
>That answer is an angle.  Multiply that by 2 to get the angle, A, at
>which each pair of the the 4 panels in the truncated pyramid meet.
>
>If this is all boogity boogity to you but yer going to try it anyhow,
>note that you may have to tell your calculator to give you the answer
>to the arcsin function in degrees, not in radians or grads.  Sine
>tables are usually in degrees, I think.
>
>If, on the other hand, this is all Mickey Mouse to you and I'm all
>wrong, show me and I'll go do penance. :-) But I did try some numbers
>and they seemed to come out about right.  As a quick check, imagine
>that S and H are equal.  Then it's a square box with vertical sides
>and A should be 90 deg.  That's what the formula gives.
>
>
>- Mike
>
>  
>